This invention relates generally to position measuring systems utilizing magnetic sensors and more particularly to a system for determining the relative position between a naval torpedo and a ferrous target and thereafter homing in on the target.
An accurate torpedo hit is now essential for modern surface ships and submarines due to recent improvements in ship construction techniques. For example, it is usually desirable for the torpedo to strike the target near its center rather than at the bow or stern so as to cause maximum damage.
Modern torpedoes typically use sonar systems to provide target relative position data for their guidance systems. At medium to long ranges, e.g. greater than 150 to 500 m, such systems are very effective. However, at near ranges, e.g. less than 150 m, target position data from sonar systems may be subject to serious errors for the following reasons. First, for an active sonar system, the transmitted and received pulses may interfere with each other due to the close proximity of the target. For a transmitted pulsewidth of 0.2 sec, for example, this presents a problem at approximately 150 m from the target since an acoustic pulse propagating at a nominal speed of 1500 m/sec in sea water takes 0.2 sec to travel the 300 m round trip to and from the target. Secondly, at near ranges, i.e. when the range is equal to or smaller than the target's maximum dimension, as can happen for typical targets at 150 m, acoustic targets typically break up into a number of spatially discrete acoustic "highlights". The torpedo is now faced with a choice of which highlight to home in on. Thus, bow and/or stern highlights can cause a torpedo to deviate from an effective central hit.
Accordingly, it is an object of the present invention, therefore, to provide an improvement in systems for providing target relative position data for an ordnance guidance system.
It is another object of the invention to provide an improved system for determining the relative position between a torpedo and a naval vessel.
It is a further object of the invention to provide a magnetic system for determining the relative position between a naval torpedo and a ferrous target for guiding the torpedo to the target at near ranges.